Delineating stainless behavior of austenitic compositionally complex alloys through CALPHAD-informed alloy design

The emergence of compositionally complex alloys (CCAs) and phase-predictive software has enabled the microstructure-informed optimization of corrosion-resistant elements to promote stainless behavior. The relatively high solubility of lightweighting elements (LWEs) Al, Si, and Ti in face-centered cubic (FCC) CCA microstructures offers a promising path toward lower-density austenitic alloys. In this work, a set of single-phase FCC alloys based on Ni₄₃Fe₃₇Cr₁₀-(Al,Si,Ti)₁₀—excluding Mn and Co—was designed using high-throughput CALPHAD modeling and fabricated via arc melting. This composition space enabled a controlled study of LWE influence on relevant properties while maintaining chemical homogeneity. LWE additions reduced density and increased hardness relative to a control alloy without LWEs, with Al and Ti producing the most pronounced effects on each property, respectively. Two key electrochemical parameters—passive film growth rate and resistance—were quantified, with Ti showing the strongest per-atom effect: a greater than 10-fold increase in film resistance and 4-fold increase in growth rate relative to the control alloy. Post-hoc XPS results and in operando tracking of elemental dissolution rates measured via AESEC suggest rapid surface enrichment by LWE, providing an explanation for the observed electrochemical benefits of LWE inclusion. Finally, unsupervised clustering analysis identified simple quantitative design rules for corrosion: Ti greater than 3 at.% promotes both fast film growth and higher passive film resistance, while Si greater than 5 at.% or Ti at 3 at.% yields rapid growth but lower resistance.